1. Field of the Invention
The present invention relates to a TCP/IP (Transmission Control Protocol/Internet Protocol) communication system, and more particularly to a communication channel releasing method at the time of non-communication in a TCP/IP communication system.
2. Description of the Related Art
Conventionally, in the TCP/IP mobile communication networks such as the Internet, the Intra-net, the Extra-net and the UNIX workstation network, a communication channel is released at the time of a final completion in a data communication caused by a key operation in a mobile communication terminal or at the time of an on-hook key operation associated with communication end.
FIG. 1 is a block diagram showing a structure of the conventional TCP/IP mobile communication network. In this TCP/IP mobile communication network, a mobile switching controller (MSC) 4 accommodates an Internet line network 1, an Internet service provider apparatus (ISP) 2 and an access server (an asynchronous serial—LAN protocol converter) 3. The Internet line network 1 includes a digital telephone line network, an analog telephone line network and a digital mobile telephone network.
Also, the mobile switching controller 4 accommodates a radio base station controller (BSC) 6 and a radio base station (BTS) 7. The radio base station 7 accommodates a mobile station (MS) 8 through a radio channel (air interface). A data terminal (DTE) 10 is connected through a data communication adapter (MS-ADP) 9 to the mobile station 8. The data terminal 10 is composed of a mobile personal computer containing a browser (application program) and the like. It should be noted that the mobile station 8 may be a portable telephone having a browser such as a portable telephone operating in an I-mode. The I-mode is information service provided by a NTT DoCoMo, Inc.
The mobile switching controller 4 includes an inter working function apparatus (HPM-IWF) 4a and a time division switch (TDNW) 4b in order to carry out a connection process to the Internet service provider apparatus 2. A call processor (CP) 4c is connected to the time division switch 4b to carry out call processing. A signal relay unit (TRK) 14 accommodates a plurality of trunk lines and is connected to the call processor (CP) 4c. 
FIG. 2 is a block diagram showing the structure of the inter working function apparatus 4a. The inter working function apparatus 4a is composed of a radio line side termination reception circuit (ARQ-RX) 11a and a radio line side termination transmission circuit (ARQ-TX) 12b for terminating a transmission error control protocol on a radio line side, and a communication line side termination transmission circuit (ASYNC-TX) 11b and a communication line side termination reception circuit (ASYNC-RX) 12a for terminating communication in a serial communication line, and a line signal circuit 13.
In the TCP/IP mobile communication network shown in FIG. 1, communication is carried out between terminals, i.e., between a communication terminal (not shown) on the side of the Internet line network 1 and the data terminal 10. The mobile switching controller 4 and the call processor 4c carry out a switching process for a process for a user data transfer channel and a control channel. In the communication between the terminals in the TCP/IP mobile communication network, the communication line is released only at the time of a final completion caused by a key operation at the communication terminal or the data terminal 10 or at the time of an on-hook key operation associated with communication end.
The plurality of signal relay units 14 are installed inside the mobile switching controller 4 to accommodate a plurality of physical lines. In some case, the plurality of signal relay units 14 may be installed outside the mobile switching controller 4. The line signal circuit 13 selects one from among the plurality of signal relay units 14. This operation corresponds to a selection of physical lines. It should be noted that, in such a TCP/IP mobile communication network, there may be a case that such a signal relay unit is also installed between the mobile switching controller 4 and the radio base station controller 6. However, the illustration for such a structure is omitted.
In this conventional TCP/IP mobile communication network, the communication line is released at the time of an on-hook key operation in the terminal. Also, it is necessary to install the plurality of signal relay units composed of the trunk circuits and physical lines in the mobile switching controller. The signal relay unit is required to be set at a usable state even at the time of a non-communication. Also, the radio line in the radio region is at a connection state. Therefore, a definite radio frequency band cannot be effectively used and also a statistically multiplexing effect due to a packet multiplexing cannot be achieved.
Also, in the conventional TCP/IP mobile communication network, the mobile switching controller selects one of the plurality of signal relay unites every call. That is, this operation corresponds to the selection of one of the physical lines. This results in the increases in the size of the apparatuses and the size of the processes.
In conjunction with the above description, “Mobile Communication Base Station, Portable Telephone Terminal And Mobile Communication System” is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei, 10-23533). In this mobile communication system, a portable telephone terminal is composed of a terminal controller for fixing/releasing a reception channel in accordance with a reception of a channel fixing/releasing control signal from a mobile communication base station and setting a non-transfer channel fixed waiting mode or a waiting mode in accordance with reception of a transmitter on/off signal. A frequency synthesizer fixes an oscillation frequency in accordance with reception of a fixed signal of a reception channel from the terminal controller. The mobile communication base station has a base station controller for establishing a call path through a common control channel. The base station controller also controls a transmission of the channel fixing/releasing control signal to fix or release the reception channel for the portable telephone terminal. Then, the base station controller controls transmission of transmitter on and off signals to turn on and off the transmission from the portable telephone terminal. Thus, a mobile communication system stops the transmission from the portable telephone terminal or turning off a power supply at a particular location without any dependence on a manual operation.
Also, Japanese Laid Open Patent Application (JP-A-Heisei, 10-112738) discloses “Data Terminal That Can Carry Out Radio Data Communication”. This data terminal contains therein a radio modem function block in which IP packet data can be automatically sent and received based on the TCP/IP protocol by using a control channel. In the radio modem function block, a signal controller controls data transmission/reception between portable telephones. A data terminal communication controller processes data from data communication software, and recognizes and outputs a modem control command. A modem control command processor receives the modem control command, and starts a packet communication interface. The packet communication interface outputs, by using the control channel, trigger signals for start and end of an IP packet data communication to the signal controller. Also, the data communication protocol processor carries out a data link procedure for the IP packet data communication. Thus, the IP packet data communication can be carried out by using the control channel between the portable telephone and a radio base station.